The last few years have seen a rapid increase in the number of unvented kerosene heaters being used by domestic consumers. Such heaters produce both odors and carbon monoxide. While the kerosene heaters commonly available vary somewhat in outward design their functions are very similar. The kerosene flame is usually on a ceramic wick and is held in a perforated container so as to trap the heat by creating a volume heated in excess of the red heat zone, i.e., over 1000.degree. F. The kerosene burns nearly to completion in such an environment. However, to limit odors and carbon monoxide emissions, the design of the heater must incorporate low thermal inertia so as to heat up and cool down fast. This low thermal inertia design sacrifices control of fuel consumption because of the constant heated volume. A design compromise thus exists in the potential for generation of appreciable odor and carbon monoxide emission in the interest of better fuel economy. Accordingly, there is a need to abate these contaminants which would otherwise be obnoxious and a hazard to persons in the vicinity of the heater, as well as potentially damaging to fabrics, household goods, and the like.
Several possible solutions to this problem were considered by the applicants herein. A trap or filter in the exhaust gas region would be impractical because a flame restricting pressure drop would be encountered in the unvented heater design. Similarly, use of renewable chemicals such as activated carbon to adsorb odors and carbon monoxide would be self-defeating to the unvented, simple kerosene heater.
Use of a catalyst was therefore suggested, as has been known previously for abatement of odor and carbon monoxide in certain kerosene heaters. However, it was determined that no previously available catalyst satisfied the goals of the invention which were to provide a retro-fittable catalyst adaptable to most, if not all, of the kerosene heaters on the market and simply installable by the consumer himself. Furthermore such a universally designed catalyst structure would desirably be retro-fittable to those few unvented kerosene heaters now sold with catalysts, for replacement of the catalyst when it no longer functions.
It is therefore an object of the invention to provide a retro-fittable catalyst for unvented kerosene heaters which fits both heaters supplied with catalysts and without, which is applicable to both radiant and convection heaters, which can be made at reasonable cost, be suitable for ready installation, and not require any additional energy or chemical reactions for reduction of odor and carbon monoxide.
A further object of the invention is to supply a catalyst as described above, and moreover having low thermal inertia, minimal pressure drop, high abatement activity for both carbon monoxide and odors, and acceptable catalyst life at low cost.
It is important that the catalyst, as noted, be of low cost. Accordingly, while the selection of a alumina/platinum group metals catalyst was a clear selection based on prior art and the prior experience of the applicants, it was necessary to avoid the use of conventional ceramic catalyst supports formed of materials such as cordierite, mullite or alumina, because these all require a container or some other means of protecting the ceramic from breaking, as well as a means of capturing enough heat from the heater to cause the catalytic reaction to take place. Such containers are generally coated metal, e.g., stainless steel, with some insulating filler between the shell of the container and the ceramic catalyst support. Such an abatement package would not be acceptable to the consumer because of high price and high thermal inertia. Such a device would also be difficult to adapt to the numerous models of kerosene heaters now on the market.
Accordingly, it is a further object of the invention to provide a simplified catalyst support structure which is inexpensive and adaptable to various models of kerosene heaters now on the market.